That coagulant appears to be old gasoline that congealed when mixed with moisture that typically gets on top of the tank. It's not uncommon. Scrape off a piece of it and smell it. If it smells like old stale gas, soften it with mineral spirits and scrape it with a plastic scraper, like a bondo squeegee or an old hotel room key, I always keep my hotel swipe keys for all kinds of projects where you don't want to gouge or scratch what you're working on. So get off all that stuff and then remove the sender and replace the gasket, next remove the fuel hose and unscrew the bayonet fitting and re seal the threads with permatex fuel system sealer, I think it is #2 but investigate that. It must be approved for gasoline. Do not use Teflon tape. This is a good time to replace your main fuel line running to the engine. You will need the thick walled 3/8 ID class 1 for under the deck. Your fuel line probably original and is overdue for replacement. You can use a bayonet double ended splice to join the old and new fuel lines together and electrical tape it together and pull the new fuel line with your old one. If you use hose clamps on the fitting and try to pull it it will get hung up in bends or old foam. Use two people pulling back and forth gently until the new hose makes its way back to the engine or fuel filter.
